fs/ntfs3: Add bitmap

// SPDX-License-Identifier: GPL-2.0

/*

 *

 * Copyright (C) 2019-2021 Paragon Software GmbH, All rights reserved.

 *

 */

#include <linux/blkdev.h>

#include <linux/buffer_head.h>

#include <linux/fs.h>

#include <linux/nls.h>

#include "debug.h"

#include "ntfs.h"

#include "ntfs_fs.h"

#define BITS_IN_SIZE_T (sizeof(size_t) * 8)

/*

 * fill_mask[i] - first i bits are '1' , i = 0,1,2,3,4,5,6,7,8

 * fill_mask[i] = 0xFF >> (8-i)

 */

static const u8 fill_mask[] = { 0x00, 0x01, 0x03, 0x07, 0x0F,

				0x1F, 0x3F, 0x7F, 0xFF };

/*

 * zero_mask[i] - first i bits are '0' , i = 0,1,2,3,4,5,6,7,8

 * zero_mask[i] = 0xFF << i

 */

static const u8 zero_mask[] = { 0xFF, 0xFE, 0xFC, 0xF8, 0xF0,

				0xE0, 0xC0, 0x80, 0x00 };

/*

 * are_bits_clear

 *

 * Returns true if all bits [bit, bit+nbits) are zeros "0"

 */

bool are_bits_clear(const ulong *lmap, size_t bit, size_t nbits)

{

	size_t pos = bit & 7;

	const u8 *map = (u8 *)lmap + (bit >> 3);

	if (pos) {

		if (8 - pos >= nbits)

			return !nbits || !(*map & fill_mask[pos + nbits] &

					   zero_mask[pos]);

		if (*map++ & zero_mask[pos])

			return false;

		nbits -= 8 - pos;

	}

	pos = ((size_t)map) & (sizeof(size_t) - 1);

	if (pos) {

		pos = sizeof(size_t) - pos;

		if (nbits >= pos * 8) {

			for (nbits -= pos * 8; pos; pos--, map++) {

				if (*map)

					return false;

			}

		}

	}

	for (pos = nbits / BITS_IN_SIZE_T; pos; pos--, map += sizeof(size_t)) {

		if (*((size_t *)map))

			return false;

	}

	for (pos = (nbits % BITS_IN_SIZE_T) >> 3; pos; pos--, map++) {

		if (*map)

			return false;

	}

	pos = nbits & 7;

	if (pos && (*map & fill_mask[pos]))

		return false;

	// All bits are zero

	return true;

}

/*

 * are_bits_set

 *

 * Returns true if all bits [bit, bit+nbits) are ones "1"

 */

bool are_bits_set(const ulong *lmap, size_t bit, size_t nbits)

{

	u8 mask;

	size_t pos = bit & 7;

	const u8 *map = (u8 *)lmap + (bit >> 3);

	if (pos) {

		if (8 - pos >= nbits) {

			mask = fill_mask[pos + nbits] & zero_mask[pos];

			return !nbits || (*map & mask) == mask;

		}

		mask = zero_mask[pos];

		if ((*map++ & mask) != mask)

			return false;

		nbits -= 8 - pos;

	}

	pos = ((size_t)map) & (sizeof(size_t) - 1);

	if (pos) {

		pos = sizeof(size_t) - pos;

		if (nbits >= pos * 8) {

			for (nbits -= pos * 8; pos; pos--, map++) {

				if (*map != 0xFF)

					return false;

			}

		}

	}

	for (pos = nbits / BITS_IN_SIZE_T; pos; pos--, map += sizeof(size_t)) {

		if (*((size_t *)map) != MINUS_ONE_T)

			return false;

	}

	for (pos = (nbits % BITS_IN_SIZE_T) >> 3; pos; pos--, map++) {

		if (*map != 0xFF)

			return false;

	}

	pos = nbits & 7;

	if (pos) {

		u8 mask = fill_mask[pos];

		if ((*map & mask) != mask)

			return false;

	}

	// All bits are ones

	return true;

}